Superbug Genome Sequenced

The genome of a newly-emerging superbug, commonly known as Steno, has just been sequenced. The results reveal an organism with a remarkable capacity for drug resistance.

Steno infections are as difficult to treat as MRSA and C.diff infections, however, Steno infections are rarer than MRSA and C.diff infections and are exclusively hospital-acquired.

Scientists at the Wellcome Trust Sanger Institute which is near Cambridge and the University of Bristol have recently sequenced the genome of this newly emerging superbug. Steno displays a remarkable capacity for drug resistance.

Dr Matthew Avison from the University of Bristol, and senior author on the paper said: “This is the latest in an ever-increasing list of antibiotic-resistant hospital superbugs. The degree of resistance it shows is very worrying. Strains are now emerging that are resistant to all available antibiotics, and no new drugs capable of combating these ‘pan-resistant’ strains are currently in development.”

Steno favours life in a moist environment around taps and shower heads, for example and can thus be readily transferred to patients.

Steno is distinct in the way that it causes infection as it can only get into the body via devices such as catheters or ventilation tubes that are left in place for long periods of time. Long-dwelling catheters are used most often for seriously ill patients and some undergoing chemotherapy.

A Steno bacterium dividing

Photo by Matthew Avison

Steno is able to stick to the catheter and grow into a ‘biofilm’. When the catheter is next flushed, the Steno biofilm can enter the patient’s bloodstream. If the patient’s immune system is impaired (which is often the case in the seriously ill and those undergoing chemotherapy) the organism can multiply and cause septicaemia.

These patients are often treated with antibiotics to which Steno is largely resistant.

Approximately 1,000 reports of Stenotrophomonas maltophilia (Steno) blood poisoning are made in the UK each year, with a mortality rate of about 30%. The organism is also found in the lungs of many adults with cystic fibrosis, and causes ventilator-associated pneumonias, particularly in elderly intensive-care patients.

There are key questions which require answers:

How does Steno stick to surfaces like catheters and ventilator tubes?

How does it form biofilms and so survive attempts to decontaminate and clean?

Why is it resistant to antibiotics?

Dr Lisa Crossman from the Sanger Institute and first author on the paper explained how the research might address these questions: “The genome sequence should help us to combat these properties. For example, if we know which proteins cause it to stick to surfaces, we could try to develop biochemical compounds that interfere with this interaction. If we understand its antibiotic resistance mechanisms, we might be able to design inhibitors that block them.”

Steno infections are still relatively uncommon but are on the increase. Furthermore, there are two other organisms that cause similar types of infections, but are more common.

Dr Avison added: “Genome sequences for these two also exist, and so now we can look at what they all have in common genetically that might explain why they are so resistant to antibiotics.”